LONG SPIN RELAXATION TIMES IN A SINGLE-BEAM BLUE-DETUNED OPTICAL TRAP

A scheme to trap atoms in a blue-detuned optical dipole trap, formed with a single laser beam and a holographic phase plate, is demonstrated. ${10}^{5}$ rubidium atoms are trapped for (1/e lifetime) \ensuremath{\sim}300 msec, at temperatures of \ensuremath{\sim}24 \ensuremath{\mu}K and a density of $\ensuremath{\sim}7\ifmmode\times\else\texttimes\fi{}{10}^{11}{\mathrm{a}\mathrm{t}\mathrm{o}\mathrm{m}\mathrm{s}/\mathrm{c}\mathrm{m}}^{3},$ for a trapping beam detuning of 0.1\char21{}30 nm. The time for a trapped atom to scatter one photon off the trapping beam is measured and found to be linear in the trapping laser detuning. At a detuning of 0.5 nm from resonance this time was measured to be \ensuremath{\sim}100 msec, indicating that the atoms are exposed on average only to \ensuremath{\sim}1/700 of the maximal light intensity in the trap. The use of a single laser beam allows for simple dynamical changes of the potential and large adiabatic compressions, while keeping the atoms mainly in the dark.